1. Field of the Invention
The present invention generally relates to a drive circuit for a solid-state imaging device. More specifically, the present invention is directed to such an image sensor driving circuit suitable for driving a solid-state imaging element requiring a higher substrate voltage "Vsub" than a voltage of a power supply used for this solid-state imaging device.
2Description of the Prior Art
In commercially available solid-state imaging elements, for instance, a CCD (charge-coupled device) image sensor, both a positive-polarity voltage "VH" having a value on the order of 15 V and a negative-polarity voltage "VL" having a value on the order of -8.5 V are utilized as a power source voltage.
In addition to this power source voltage, a proper substrate voltage "Vsub" must be set in such a CCD image sensor having such a structure that an n-type substrate is employed as an overflow drain. There are possibilities that this substrate voltage "Vsub" must be selected to be higher than the positive-polarity voltage "VH".
Accordingly, in the conventional CCD image sensor which requires the higher substrate voltage "Vsub" than the positive-polarity voltage "V.sub.H ", as shown in FIG. 1, the following substrate voltage setting arrangement is employed. That is, the Vsub power source 21 having the source voltage on the order of 20 V, is employed, and in the substrate voltage setting circuit 17' constructed of the operational amplifier 20 whose drive voltage is equal to the source voltage applied from the Vsub power source 21, the desirable substrate voltage "Vsub" is set based on the reference voltage "Vref" produced by controlling the variable resistor "VR".
As previously described, in the conventional CCD image sensor, the Vsub power source 21 exclusively used to set the substrate voltage Vsub higher than the positive-polarity voltage V.sub.H must be employed in the conventional CCD drive circuit. As a consequence, there is such a problem that when this CCD drive circuit would be formed as an integrated circuit (IC), a volume of the external circuit should be necessarily increased.